Volume control for radio receivers



VOLUME CONTROL FOR RADIO RECEIVERS Filed May 11, 1958 3 Sheets-Sheet l4.146- VOL /36E 593 INVENTORJ m WWW 750/004- BY a 405 I I I July 9,1940- R. H. PRATT VOLUME CONTROL FOR RADIO RECEIVERS Filed May 11, 19383 Sheets-Sheet 2 INVENTOR. BY WWW 152 my 1940., R. H. PRATT VOLUMECONTROL FOR RADIO RECEIVERS 3 Sheets-Sheet 5 Filed May 11, 1938 Tar-1UINVENTOR. fa jf fidxf Patented July 9, 1940 UNITED STATES PATENT OFFICE7 2,207,023 I. VOLUME CONTROL FOR RADIO RECEIVERS Robert H. Pratt,Milwaukee, Wis.

Application May 11, 1938,;Serial No. 207,357 v 14 Claims. (o1. 25 0;2 0)

This invention relates to electrical apparatus Another object of thisinvention is to provide an adjustable volume control device for signaltransmitting circuits, said volume control device employing anadjustable resonant circuit adapted to control the signal volume in acontinuousand gradual manner not accompanied by disturbances introducedinto the circuit by conventional variable resistance type controls.

A further object of this invention is to provide a volume controladapted to be employed with a pretuned amplifier, such as, theintermediate frequency amplifier of a superheterodyne receiver, saidvolume control consistingof a series resonant circuit adapted to beadjusted to be resonant at or near the signal frequency so that theoutput of said amplifier may be easily and efiiciently controlledwithout introducing undesirable disturbances into the circuits of theamplifier.

Other and further objects of this invention 'will be apparent from thefollowing specification and claims.

In accordance with this invention I provide a volume control which maybe used conveniently with amplifiers and signal transmission systems ofthe high frequency type which are tuned or adjusted to amplify ortransmit a predetermined set of high frequencies or band of frequencies.The volume control of my invention consists essentially of one or moreseries resonant circuits, each of which consist of an inductance and anadjustable condenser. The inductance may, of course be made variable,one form which may be variometer or a variable core inductance ifdesired, although I prefer to employ a variable condenser and a setinductance coil. 7

I am aware of the numerous uses-to which series resonant circuits havebeen placed since the phenomenon of resonancein' electrical circuitsincluding inductance and capacity'was discovered.

I am also familiar with the vario'us Y receivers.

, trol hasbeen in-long and continuous use.

types of devices used for volume controls in radio The manualyadjustable types of volume controls generally employ a Variable resistorconnected as a potentiometer into different parts H of the amplifiercircuit. This type of volume "'5 control has numerous disadvantages anumber of which my invention has overcome. For example, the volumecontrol of my invention does not require the use of sliding contacts asdoes a variable resistance device Consequently the likelihood ofproducing poor and noisy contacts is avoided even in cases where thevolume con- The volume control of my invention also may be employed as atone compensating device since al- '15 tering the LC ratio may be madeto eliminate,

first the high frequencies and then the low frequencies of one of theside bands, gradually as the value of the capacity C is increased.

Numerous other advantages are inherent in my invention. These will beapparent from the following specification includingthe description ofthe drawings in which, briefly, Fig.'=1 illustrates a schematic diagramof an embodiment of my invention; Figs. 2,3, 4 and 5 are schematicdiagrams used to facilitate the explanation of this invention; Fig. 6 isa modified form of my invention; Fig. '7 is another modified form of myinvention; Fig. 8 illustrates another embodiment 'ofthis invention; Fig.9 shows an embodiment of-this invention applied to energize" and controlpotentials on grid electrodes of a volume expander tube; Fig. 10 showsanother embodiment of this invention in which the manual volume con-'trol device is employed to control the potential 3 across a rectifieror detector tube arranged to provide both a positive and a negative biasor potential derived from a signal; and Fig. 11 illustrates a practicalembodiment of a condenser and'inductance unit which may be employed inaccordance with this invention.

' -'"R,eferrin g to Fig. 1 of the drawings in detail reference numeralIll designates one of the intermediate frequency amplifier tubes of asuperheterodyne receiver. This tube may be of the type-sold under thedesignation 6K7 or 58. It is of courseobvious that the receiver may em-;ploy one or more tubes in the intermediate frequency'amplifier and thatthis amplifier is designedto amplify a certain frequency band se- 5-lectively as is well known in the art. The anode ""o'fthe tube I0 isconnected "by the wire II to the 0 primary inductance l2 of thetransformer l3, and tothe'condenser l5. This condenser l5'is connectedto-the grid 16 of the. tube H which is of the duplex diode pentode typesold as type 2B? and is in this case employed as a separate automaticvolume control. This tube is provided with the grid electrode l6, screenelectrode 2|, suppressor electrode I9, plate electrode 20, cathode l8,diodes 23 and cathode heater 22. The grid I6 is also connected to oneend of the resistor 25, the other end of which is connected to thechassis or ground 24. A positive potential is applied to the screenelectrode 2| and this potential may be derived from a source ofrectified alternating current which also may be employed for energizinganode, screens and grid bias circuits of various tubes of thesuperheterodyne receiver, if desired.

A by-pass condenser 26 is connected to the screen electrode 2| and tothe chassis, that is, the common ground to by-pass signal alternatingcurrents from the power supply circuit. The anode 20 is connected to theprimary '28 of the transformer 21 and the primary and secondary aretuned, the former by the condenser 29 and the latter by condenser 3!.

The diodes 23 are employed in this case as part of the rectifier forrectifying the current flowing through the potentiometer 32 of theautomatic volume control circuit. A variable contact 34 is provided tothe potentiometer 32 and this contact is connected to the grid circuitsof tubes of the superheterodyne receiver which are to have gridelectrodes biased in accordance with potential derived from theautomatic volume control circuit. One end of the potentiometer 32 isconnected to the inductance 30 and the other end is connected to thecommon ground .or chassis. A condenser 33 is connected across theresistance element of the potentiometer to bypass high frequencycurrents across the element and thereby prevent high. potential highfrequency currents from affecting the operation of the device.

A positive potential source is connected to the inductance 28 toenergize the anode of the tube ll. This source of current supply may bethe same as that employed for the screen 2|.

The detector tube 35, employing a pair of diodes 3'! and an indirectlyheated cathode, is connected to the secondary H! which is shunted by atuning condenser M. A resistor 42, by-passed with a condenser 43, isconnected to one end of the tuned circuit including the secondary l4 andcondenser 4|, and the other end of this tuned circuit is connected tothe diodes 3'! and the variable condenser 40 of the volume controlcircuit 38. The condenser 46 is connected to the inductance 39 which inturn is connected to the resistor 42 and the secondary M. The cathode ofthe tube 35 is connected to the chassis as is also the resistor 42.

The portion of the receiving circuit showing the principal connectionsof the diode detector 35 and the volume control circuit employing thecondenser 39 and the capacity 40 are illustrated in Figs. 2 and 4. Theequivalent electrical network diagram shown in Fig. 3 illustrates theoperation of this volume control when employed in the circuitarrangement shown in Fig. 2. When the volume control circuit is modifiedas shown in Fig. 4 the equivalent electrical network shown in Fig. 5applies. In Fig. 3, E0 designates the input voltage impressed upon thesecondary M. The inductance of this secondary is indicated by Lo and theresistance is indicated by R0. The

condenser 4| which is connected across the secondary I4 is designated byC1 and .theresistance capacity 40.

of this condenser is designated by R1; the impedance of this branch isdesignated by Z1. The volume control branch of the circuit including theinductance 39 and the condenser 49 is divided into inductance L2,resistance R2 and capacity C2; the impedance of this combination isdesignated as Z2. The diode detector 35 having impedance Rd is in effectconnected in series with the resistance and capacity parallel circuit42, 43. Thus the diode detector and the parallel circuit 42, 43 form ashunt across the inductance-capacity volume control circuit 39, 49.

From a mathematical analysis of this circuit it can be shown that thevolume of the high frequency signal across the output impedance Z3 canbe controlled by the volume control circuitforming the impedance Z2. Theattenuation obtained for different settings of the variable condenser 40can be predetermined and attenuation curves of any desired shape orshapes can be obtained simply by changing the shape of the rotor andstator plates of the condenser 40.

The Values of the volume control elements 39 and 40 depend, of course,upon the frequency to which the intermediate frequency amplifier, orother substantially fixed frequency amplifier with which the inventionis employed, is tuned. Various values of capacity and inductance havebeen employed in the volume control disclosed herein with asuperheterodyne receiver having an intermediate frequency of 465kilocycles. The best results were obtained using a radio frequency chokecoil having an inductance of 2.5 millihenrys as the inductance 39. Thischoke coil was made up of four spaced honey-comb wound coil sectionsconnected in series. A micro-microfarad variable condenser was employedas the By employing this combination series resonant could be readilyobtained at the intermediate frequency of 465 kilocycles and the volumeof the superheterodyne receiver could be accurately and easilycontrolled from low to high intensities and also intermediateintensities.

In order to simplify the installation of this Volume control device thecircuit illustrated in Fig. 4 was developed. This circuit issubstantially the same as the circuit shown in Fig. 2 except that thevolume control is connected across the diode .detector 35, theinductance 39 being connected to the diodes 3! and the rotor plates ofthe condenser 49 being connected to the chassis and the cathode 36 ofthe tube 35. By employing this connection the operator can adjust thevariable condenser 40 without introducing the effects of body capacityinasmuch as the rotor of this condenser is connected to the metalchassis of the radio receiver direct. The equivalent electrical networkthat is applicable to this circuit is shown in Fig. 5 and from this itWill be observed that the parallel circuit formed by the volume controland the diode detector 35 is connected in series with the parallelcircuit formed by the resistance 42 and the condenser 43. This complexseries circuit is connected across the tuned secondary M. The outputcircuit is connected across the impedance Z3 as before.

The circuit illustrated in Fig. 4 requires a condenser 49 of larger sizethan that required in the .arrangement shown in Fig. 2 to produceminimum volume in the output of the radio receiver. The circuitillustrated in Fig. 4 however results in a simpler device as far as itselectrical connections are concerned since the condenser shaft can begrounded to the chassis of the radio receiver and the condenser andinductance arrangement 75 atoms placedin a single shield container. Theinductance is then connected to the diodes 31 by a single wire which maybe shielded if necessary.

In the development of the embodiment of this invention shown in Fig. 4the inductance 39 was made substantially larger than that employed inthe embodiment shown in Fig. 2. The purpose of making the inductance 39as large as possible, consistent with producing the desired results, isto permit the use of a relatively small capacity condenser 40. By makingthe inductance 39 approximately twice as large as that described inpreceding paragraphs in connection with the description of Fig. 2, acondenser of approximately micro-microfarad maximum capacity was foundto be sufficientto produce a condition of series resonance at' theintermediate frequency of the superheterodyne amplifier. Thus thisvolume control would produce a condition of minimum output in the radioreceiver when the condenser 40 is adjusted substantially to maximumcapacity, that is, when a condition ofseries resonance was obtained.Maximum output would therefore be produced when the volume controlcondenser was adjusted to substantially minimum capacity. This isdesirable since the value of the tuning condenser 49 connected acrossthe secondary I4 can be adjusted to pea the intermediate frequencytransformer at the intermediate frequency more readily under theseconditions. tuning of this intermediate frequency transformer secondary14 must be adjusted after the volume control 38 is connected into thecircuit.

'After the volume control is connected into circuit and the secondary I4is tuned, adjustment of the condenser 49 may be necessary to compensatethe variations in inductance and capacity of the elements of the volumecontrol, however this is accomplished in a simple manner by mounting thevolume control in a metal can to shield the control effectively. Meansis also provided for changing the relation of the stator plates of thecondenser with respect to the metal shield to adjust the maximumcapacity. If desired the inductance also may be made adjustable withrespect to the metal shield.

It will be observed that various values have been given for theinductance and capacity of the volume control elements. These are, ofcourse, given only for the purpose of illustration and it is notintended that this invention is operable only when those values areemployed. The values of inductance and capacity employed depend upon therange of control desired and the frequency at which the control is to beoperated. Furthermore it may be desirable to employ inductance unitsprovided with cores of magnetic material, such as are now employed inintermediate frequency transformers. On the other hand the inductanceunit 39 may be made variable instead of the condenser 40 and a suitablevariometer construction employed. If desired the condenser 40 may bedivided into two sections, only one of which is variable, and these twosections connected in series, one on each side of the inductance 39.Other combinations may include the use of the inductance 39 and thecapacity 40 circuit as shown in Figs. 2 and 4 and another con-- denserof suitable size may be shunted across both the inductance 39 and thecapacity 49. It will therefore be observed that various combinations maybe employed in the volume control of my It should be borne in mind thatthe rangement is illustrated in Fig. 6 in which two series resonantcircuits connected in parallel are employed. The purpose of thisarrangement is to lower the resistance of the volume control circuit tothe radio frequency potential when the volume control is in a conditionof series resonance to the frequency of the radio frequency potential.When the volume control circuit is in resonance with the signalfrequency the signal voltage across the volume control circuit will bethe potential drop due to the ohmic resistance of the coils orinductance windings at the signal frequency. In order to obtain as greata range of control as possible the ohmic resistance of these coilsshould be made as low as possible consistent with proper design. It isof course possible and in some cases may be desirable to make each ofthe series circuits comprising the parallel volume control circuitarrangement shown in Fig.

6, of slightly different frequency characteristics so that only one ofthe parallel branches will actually be in series resonance at anyparticular frequency and it is of course not desired to limit thisinvention to an arrangement in which the '7 parallel branches areexactly alike since a condition such as this might be difiicult toobtain in practice.

Where it is desired tobe able to control the volume of radio stations ofsubstantial power 7 located in close proximity to the radio receivingset employing the volume control of my invention, a circuit such asillustrated in Fig. 7 has proved very satisfactory. This circuit employsa series volume control, such as shown in Fig. 4

including an inductance coil 39 and a variable condenser 49 connected bymeans of a wire 50, which is provided with a grounded shield 5|, to thediodes of the tube 35. In this case the volume control includes anotherseries resonant circuit made up of the inductance 52 and the variablecondenser 53. The variable condenser 53 is connected to the variablecondenser 49 and to the metal chassis of the radio receiving appa ratusby means of the wire 54. The inductance 52, is connected by the wire 55which is shielded 7 by the hollow conductor 56, to the grid 58 of thesecond intermediate frequency amplifier 51. The condensers 40 and 53 maybe controlled by a single shaft or other gang control arrangement,

if desired. It will be observed from the circuit 4 diagram illustratedin Fig. '7 that the intermediate frequency amplifier of thesuperheterodyne receiver consists of the first, second and thirdintermediate frequency amplifier tubes which are of the screen grid typeand which are connected in cascade.

The condensers 40 and 53 are preferably of the twin straight linefrequency type each having a maximum capacity of 150 micro-microfaradsand the inductance units 31 and 52 each consist of multi-sectionwindings in which each section is a small honey-comb coil. Theinductance of each of the inductance units is slightly over 2millihenrys. These values are satisfactory where the intermediatefrequencyto which the amplifier is adjusted is 465' kilocycles.

In operation the secondary I4should be tuned by the condenser H to themaximum volume, that.

is the circuit including this secondary I4 and the condenser 4| shouldbe tuned to parallel resonance at the intermediate frequency so that theoutput of the amplifier will be substantially max-- imum when thecondenser 40 is set at minimum capacity. The circuit of the secondary 60and the condenser'59," onthe other hand should be tuned so that maximumvolume is obtained when the condenser 53 is set at about one-half of itsfull capacity. If this procedure is not followed side band interferencemay be obtained when signals from a weak station are being received anda strong station is transmitting on a frequency adjacent to that of theweak station. This is caused by detuning influence of the condenser 53on the tuned circuit including the condenser 59 and secondary inductance6!]. In practice it was found that the capacity of the condensers 45 and53 affected less detuning of the secondary circuits of the intermediatefrequency transformers to which the volume control is connected whencondensers of 50 micro-microfarad capacities were employed as thecondensers 40 and 53 than when these condensers were of 150micro-microfarad capacity.

The volume control connected as shown in Fig. '7 affects the separateautomatic volume control apparatus inasmuch as it decreases the actionof the automatic control as the signal volume is lowered. Nounsatisfactory results appeared from this however, and it is thereforepossible that the automatic volume control and detection can be combinedin the same tube. The volume control of this invention may of course bearranged in the circuit of the receiver so that reduclng the signalvoltage with the manually operated volume control would have no effecton the automatic volume control voltage and the amplification of the setwould not increase, through the operation of the automatic volumecontrol, as the manual volume control is operated. This may beaccomplished by taking the automatic volume control voltage from theplate of the last intermediate frequency amplifier, rectifying thisvoltage by one diode and using it in the conventional manner. The otherdiode in this case is used as a signal detector with the resonant volumecontrol of my invention connected across it. In this case reducing thesignal voltage by the manual volume control would have no effect on theautomatic volume control voltage.

In the arrangement of my invention shown in Fig. 2, for example, theresistor 42 connected between the secondary M and the metal chassis ofthe receiving set may be connected between the diodes 37 and the volumecontrol inductance 39 so current passing through the diode circuit wouldhave to pass through this resistance. In this case the secondary I4 isconnected direct to the metal chassis anda coupling condenser isprovided between the audio frequency amplifier and the conductorconnecting the inductance 39 to the condenser 45 and the secondary Hi.This arrangement is very desirable inasmuch as the size of the condenser49 of the volume control may be reduced considerably.

In Fig. 8 I have shown a slightly modified form of this invention inwhich the LC circuit including the secondary M and the tuning condenser4| is connected to the chassis or ground as shown and the cathode 36 ofthe tube 35 is connected to the chassis or ground through the resistance32 shunted by the condenser 43. The cathode 36 is connected to theintermediate frequency or audio or low frequency circuits of the signalapparatus through the coupling condenser 35a. The circuitarrangement'shown in Fig. 9 illustrates an embodiment similar to thatshown in Fig. 8 adapted for use with a volume expander circuit employinga 6L7 type of tube 10. The grid electrodes H and 12 of the tube 10 arecoupledto suitable current supply sources for biasing or other purposesby the resistors '15 and 16, respectively. The resistor 13 and condenser14 are employed for coupling or connecting the electrodes ll and 12,respectively, to the cathode 36 of the detector or rectifier tube 35.The circuit shown in Fig. 10 illustrates an embodiment of this inventionemploying a tube 35 in which the anode 37, associated with the cathode36, is connected to the cathode 36a which is associated with the anode31a. The anode 3'! and cathode 36a are connected together and to theinductance 39 of the volume control. This circuit is particularlyadapted for use in cases where it is desired to impress positive and/ornegative potentials derived from a signal upon amplifier circuits. Acoupling condenser 36c and resistors 36c and 36 are connected to thecathode 36 for this purpose and a coupling condenser 37c and resistor37?) are connected to the anode 31a for this purpose. The rectifiedvoltages derived from tone, fidelity, or anywhere a voltage proportionalto signal intensity and volume are desired.

In Fig. 11 I have illustrated an embodiment of this volume control whichis adapted for use in a circuit such as illustrated in Fig. 4 whereinthe condenser 40 may be grounded to the metal chassis of the radioreceiving apparatus. The arrangement shown in Fig. 11 employs acondenser having a shaft 450; connected to the metal shield 4022 whichis connected to the metal chassis of the receiving set. The rotor platesof the condenser are mounted on the shaft a and may be rotated bymanipulating the knob 400. The stator plates are carried by a suitablemetallic member 4011 which is attached to the insulation strip 40a Wheredesired the bolts 40h which fasten the condenser frame to the bottom ofthe can may be made slidable in slots provided in said can and byloosening these bolts the condenser may be slidably adjusted withrespect to the can to adjust the maximum capacity of the condenser. Itis of course obvious that various expedients may be employed to adjustthe maximum and minimum capacities of this condenser; different methodsmay be found more desirable in different arrangements and I do nottherefore desire to limit this invention to use with condensers of thetype illustrated in Fig. 8.

In manufacturing the volume control of my invention to be sold as a unitit may of course be desirable to mount the inductance coil 39 inside ofthe same shielding can with the condenser and in that case a smallbracket 39c may be attached to the frame of the condenser for holdingthe insulation support 391) of the inductance coil. Where desired thesupport 39b may include a metallic core of magnetic material such as isnow provided to intermediate frequency transformer windings. Furthermorethis support 395 may be made longer in order to receive a plurality ofcoil sections which are to be connected in series. One end of the coil39 is connected by means of the wire 39a, to the stationary plates ofthe condenser and the other end of the coil is connected to the diodesof the tube 35.

Numerous modifications within the spirit and scope of my invention mayof course be made and I do not therefore desire to limit this inventionto the exact details shown except in so far as those details may bedefined by the-claims.

I claim:

1. A volume control for a radio receiver of the superheterodyne type,comprising: an inductance element and a capacity element connected inseries, an intermediate frequency amplifier for the superheterodynereceiver, a rectifier connected to theoutput of said intermediatefrequency amplifier, means for connecting said inductance and capacityelements across said rectifier, and means for varying the impedance ofone of said elements whereby the ratio of the impedances of saidelements to one another may be changed gradually for varying the outputof the circuit of said rectifier.

2. A volume control for a radio receiver of the superheterodyne type,comprising: an inductance element and a capacity element connected inseries, means for connecting said series connected inductance andcapacity elements to the intermediate frequency amplifier of thesuperheterodyne receiver for impressing signal potentials across saidseries connected elements, means for varying one of said elements forgradually varying the ratio between the impedances of said elementswhereby the impedances of said elements may be gradually brought into apredetermined ratio such that the output of the intermediate frequencyamplifier may be controlled.

3. A volume control for a radio receiver of the superheterodyne type,comprising: an inductance element and a capacity element connected inseries, an intermediate frequency amplifier for the superheterodynereceiver, said amplifier comprising at least one amplifier tube and atuned transformer connected to the output of said amplifier tube, arectifier connected to the secondary of said tuned transformer, meansfor connecting said inductance and capacity elements across saidrectifier, and means for varying the impedance of one of said elementswhereby the ratio of the impedances of said elements to one another maybe changed gradually for varying the output of the circuit of saidrectifier.

4. A volume control for a radio receiver of the superheterodyne type,comprising: an inductance element and a capacity element connected inseries, means for connecting said series connected inductance andcapacity elements to the intermediate frequency amplifier of thesuperheterodyne receiver for impressing signal potentials across saidseries connected elements, means for varying one of said elements forgradually varying the ratio between the impedances of said elementswhereby the impedances of said elements may be gradually brought intoseries resonance at the intermediate frequency of said amplifier wherebythe output of the intermediate frequency amplifier may be controlled.

5. A volume control for a radio receiver of the superheterodyne type,comprising: an inductance element and a capacity element connected intoa series circuit, an intermediate frequency amplifier for thesuperheterodyne receiver, a rectifier connected to the output of saidintermediate frequency amplifier, means for connecting said seriescircuit across said rectifier, and means for tuning said series circuitwhereby the ratio of the impedances of said elements to one another maybe changed gradually up to a condition of series resonance for varyingthe output of the circuit of said rectifier.

6. A volume control for a radio receiver of the superheterodyne type,comprising: an inductance element and a capacity element connected inseries, means for connecting said series connected inductance andcapacity elements to a tuned stage of the intermediate frequencyamplifier of the superheterodyne receiver for impressing signalpotentials across said series connected elements such that the output ofsaid amplifier may be determined by the overall impedance of said seriescircuit, andmeans for varying one of said elements for gradually varyingthe ratio between the impedances of said elements whereby the impedancesof said elements may be gradually brought into a predetermined ratio.

7. A volume control for an amplifier of the type adapted to amplifydesired signals in a setfrequency band, comprising: an inductanceelement and acapacity element connected into a series circuit, meansincluded in one of said elements for varying the ratio between-theimpedances thereof whereby said series circuit may be brought to seriesresonance at a frequency in the band to which said amplifier is adjustedand connections for impressing desired-signal currents havingfrequencies within said band upon said series circuit whereby theeffective potential of said desired-signal currents may be controlled.8. A volume control for an amplifier of the type adapted to amplifydesired signals in a set frequency band, comprising: an inductanceelement and a capacity element connected into a series circuit, meansfor varying said capacity whereby said series circuit may be broughttoseries resonance at a desired-signal frequency in the band to which saidamplifier is adjusted and connections for impressing desired-signalcurrents having frequencies within said band upon said series circuitwhereby the effective potential of said desired-signal currents may becontrolled,

9. A volume control for an amplifier of the type adapted to amplifydesired signals in a set frequency band, comprising: an inductance and acapacity, connections for connecting said inductance and said capacityinto a series circuit and for connecting said series circuit across aportion of the circuit of the amplifier havingadesired-signal potentialdifference thereacross corresponding to at least one of the frequenciesof the set frequency band, and means for adjusting said series circuitto resonance to control the magnitude of said'desired-signal potentialdifference.

10. A volume control for an amplifier of the type adapted to amplifydesired signals in a set frequency band, comprising: an inductanceelement and a capacity element connected into a series circuit, meansincluded in one of said ele- .ments for varying the ratio between theimpedances thereof whereby said series circuit may be brought to seriesresonance at a desired-signal frequency in the band to which saidamplifier is adjusted and means for connecting said series circuit tosaid amplifier for impressing desiredsignal currents having frequencieswithin said band upon said series circuit for'controlling the effectivepotential of said desired-signal currents across the output circuit ofsaid amplifier.

11. A volume control for an amplifier of the type adapted to amplifydesired signals in a set frequency band, comprising: an inductance and acapacity, connections for connecting said inductance and said capacityinto a series circuit and for connecting'said series circuit across aportion of the circuit of the amplifier having a desired-signalpotential difference thereacross corresponding to at least one of thefrequencies of the set frequency band, and means for'controlling theoverall impedance of said series circuit whereby the magnitude of saiddesired-signal potential difference across said series circuit and theoutput of said amplifier may be controlled.

12. A volume control for a radio receiver of the superheterodyne type,comprising: a pair of series circuits each including an inductanceelement and a capacity element, an intermediate frequency amplifier forthe superheterodyne receiver, a rectifier connected to the output ofsaid intermediate frequency amplifier, means for connecting one of saidseries circuits across said rectifier, means for connecting the other ofsaid series circuits across a tuned circuit of said intermediatefrequency amplifier, means for varying the impedance of one of saidelements ineach of said series circuits whereby the ratio of theimpedances of said elements to one another, in each of said circuits,may be changed gradually for varying the output of said amplifier.

13. A volume control for a radio receiver of the superheterodyne type,comprising: a pair .of series circuits each including an inductanceelementand a capacity element, means for connecting each of said. seriesconnected circuits to the intermediate frequency amplifier of thesuperheterodyne' receiver for impressing signal potentials fromdifferent circuits of said amplifier across each of said seriescircuits, means for varying one of said elements in each of saidcircuits whereby said circuits may be gradually brought intoseriesresonance at the intermediate frequency of said intermediatefrequency amplifier to control the output thereof.

14. A volume control for a radio receiver of the superheterodyne type,comprising: a pair of series circuits each including an inductanceelement and a capacity element, an intermediate frequency amplifier forthe superheterodyne receiver, said amplifier including at least oneamplifier tube and tuned input and output circuits, a rectifierconnected to said output circuit, connections for connecting one of saidpair of series circuits to said rectifier. and connections forconnecting the other of said series circuits to one of said tunedcircuits connected to said amplifier whereby the output of saidamplifier may be gradually and uniformly controlled when said seriescircuits are adjusted to a condition of series resonance at theintermediate frequency of said intermediate frequency amplifier.

ROBERT H. PRATT.

